[FFmpeg-devel] [PATCH] RDFT for Bink audio

[Alex Converse]

On Fri, Jan 16, 2009 at 5:00 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Fri, Jan 16, 2009 at 02:19:15PM -0500, Alex Converse wrote:
>> On Thu, Jan 15, 2009 at 2:03 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> > On Thu, Jan 15, 2009 at 11:52:20AM -0500, Alex Converse wrote:
>> > [...]
>> >> +int ff_rdft_init(RDFTContext *s, int nbits, int inverse)
>> >> +{
>> >> +    int n = 1 << nbits;
>> >> +    int i;
>> >> +    const double theta = (1-2*inverse)*2*M_PI/n;
>> >> +
>> >> +    s->nbits = nbits;
>> >> +    s->inverse = inverse;
>> >> +
>> >> +    if (ff_fft_init(&s->fft, nbits-1, !inverse) < 0)
>> >> +        goto fail;
>> >> +
>> >> +    s->tcos = av_malloc((n>>2) * sizeof(FFTSample));
>> >> +    if (!s->tcos)
>> >> +        goto fail;
>> >> +    s->tsin = av_malloc((n>>2) * sizeof(FFTSample));
>> >> +    if (!s->tsin)
>> >> +        goto fail;
>> >> +    for (i = 0; i < (n>>2); i++) {
>> >> +        s->tcos[i] = cos(i*theta);
>> >> +        s->tsin[i] = sin(i*theta);
>> >> +    }
>> >
>> > we have a large number of sin and cos tables already
>> > see ff_sine_* / ff_cos_*, no need to duplicate them in each context
>> >
>>
>> I agree with that in principle, but in practice It doesn't seem
>> practical at the moment.
>
>> They are defined in different files,
>
> it should be very easy to split the tables out into their own file and
> add dependancies to the Makefile
>
>
>> available in different sizes.
>
> not sure if i understand you but i dont see the difference
>
>
>> The sines seem to be at half at a half
>> sample offset from what I need.
>
> indeed, ive missed that
>
>
> still even if they wouldnt be shareable though i still think cos is,
> then at least the same system of global shared tables should be used instead
> of duplicating them per context.
>

I'm looking at fft.c and those tables are a mess. Depending on the
type of fft, different tables get initialized (exptab vs ff_cos_*).
The exptab tables aren't shareable because they are half the needed
size. Even if it isn't used exptab is still allocated.

If the tables get presented in a usable fashion I will use them. I
have no current desire to re-factor fft.c, because I don't want to
deal with benchmarking such an important chunk of code.

--Alex